1. Field of the Invention
The present invention relates generally to organic electroluminescent displays, and more particularly to a structure of a cathode rampart of an organic electroluminescent display.
2. Description of the Related Art
With the advent of the information technology age, there is an increasing demand for high-quality electro-optical displays, in which liquid crystal displays (LCD) are the most popular. A LCD backlight module comprising a light guide and a reflective plate is utilized for introducing the light beams, emitted from the cold cathode fluorescent lamp, vertically to the liquid crystal display panel, in which the liquid crystal contained therein controls the illuminance of the LCD. Conventional LCD has a limited view angle and requires very complicated manufacturing processes, which result in high manufacturing costs and relatively low yields. However, organic electroluminescent displays (OELD) have larger view angle and can be produced through less complex manufacturing process. These advantages are based on the self-luminance of the organic elements in the organic electroluminescent displays, which results in the unrestricted visual angles, more natural colors displayed, increased operational temperature range and shorter response time.
Organic electroluminescent displays generally include cathodes, organic electroluminescent materials and anodes, which are stacked in sequence on a substrate of glass. The cathodes and the anodes are respectively composed of a plurality of electrodes disposed in a parallel stripes formation, and the cathodes and anodes are configured perpendicular to each other. Organic electroluminescent materials are disposed at the intersections of the cathodes and the anodes, and are separated by insulating materials. Accordingly, the cathodes, the organic electroluminescent materials and the anodes form a three-layer structure disposed on the substrate. When a voltage difference between the cathodes and the anodes is present, the organic electroluminescent material emits light beams.
The metal electrodes of the cathodes are coated through evaporation on the organic electroluminescent material after the organic electroluminescent material and the insulating materials are formed. However, the cathodes composed of metal electrodes are easily diffused along the gaps between the organic electroluminescent material and the insulating materials during the formation step. Once the cathodes contact the anodes, it will short circuit and the organic electroluminescent materials between the cathodes and the anodes can not emit light.
If foreign particles fall aside the insulating materials as defects before the electrodes of the cathode are formed by coating through evaporation, metal materials will be formed around the foreign particles during the formation step and a short circuit is likely between neighboring metal electrodes.
Furthermore, during the manufacturing process of full-color organic electroluminescent displays (FOELD), it is necessary to utilize shadow masks for partially masking the organic electroluminescent material. After the organic electroluminescent material layer for emitting light beams of one color is coated on the anodes, the shadow masks are moved so as to form another organic electroluminescent material layer for emitting light beams of another color. In this case, the shadow masks will contact the insulating materials directly during the formation of the second organic electroluminescent material layer. This will cause the insulating materials to be peeled off and deteriorate the organic electroluminescent material.
In the prior art, forming a plurality of cathode ramparts in the direction perpendicular to anode electrodes to separate cathode electrodes arranged in parallel from each other is disclosed. With the exposure at the side of the cathode ramparts, since the exposure is focused mostly at the upper portion of the cathode ramparts, the portion of the cathode ramparts adjacent to the anode electrodes is not of sufficiently cross-linking and consequently the mechanical performance thereof is not significantly high. This results in the cathode ramparts being easily peeled off while contacting the shadow masks due to the deterioration of the adhesion between the ramparts and the substrate.
If the adhesion between cathode ramparts and substrate is strengthened by revising the parameters in photolithography process, the geometry of the cathode ramparts can not be effectively used as a mask during the coating of the cathode electrodes through evaporation.
In view of the above problems, the principal object of the present invention is to provide an organic electroluminescent display and a method for manufacturing same, which prevents the anode and the cathode from defects and short circuit, and with the suitable geometry of the electrical insulation ramparts, the mechanical properties of the cathode insulating ramparts are increased such that the adhesion between the cathode insulating ramparts and the substrate is enhanced.
To achieve this object, the present invention provides an organic electroluminescent display, comprising a plurality of first display electrodes disposed in parallel on a substrate; a plurality of second display electrodes arranged in parallel, disposed on the first display electrodes and being perpendicular thereto; a plurality of organic electroluminescent materials disposed between the first display electrodes and the second display electrodes for emitting light and electrical insulation between the first and second display electrodes; a plurality of insulating ramparts disposed between neighboring two second display electrodes and arranged in parallel thereto; and overhangs disposed on the portion of the insulating ramparts away from the substrate, the portion of the insulating ramparts proximate to the substrate having a sufficiently high cross-linking such that better adhesion between insulating ramparts and the first display electrodes is ensured.
The present invention also provides a method for manufacturing an organic electroluminescent display, comprising the steps of forming a plurality of first display electrodes of high light transmission arranged in parallel on a transparent substrate; forming an insulating layer on the transparent substrate, the insulating layer including a plurality of slots perpendicular to the first display electrodes for exposing the first display electrodes; forming cathode ramparts on the exposed first display electrodes, the portion of the cathode ramparts away from the substrate providing overhangs of greater width, and the portion of the cathode ramparts proximate to the substrate having sufficiently high cross-linking for increasing the adhesion between the cathode ramparts and the first display electrodes; removing the insulating layer partially by means of the masking effect of the overhangs of the cathode ramparts for exposing the first display electrode; forming an organic electroluminescent material on the exposed first display electrodes; and forming a plurality of second display electrodes on the organic electroluminescent material.
It should be noted that the step of forming the insulating ramparts may further comprise the steps of forming a blanket of photosensitive material on the insulating layer; illuminating the photosensitive material from one side of the substrate opposite to the first display electrodes with the insulating layer as photo masks; and proceeding a development process to the photosensitive material to expose the insulating layer. Since the light beams are from the side opposite to the first display electrodes, the cross-linking at the portion of the insulating ramparts proximate to the substrate is more significant than at the portion away from the substrate. Therefore, the adhesion between the ramparts and the substrate is enhanced.
The present invention further provides a method for manufacturing an organic electroluminescent display, comprising the steps of forming a plurality of first display electrodes of high light transmission on a transparent substrate; forming an opaque insulating layer on the transparent substrate, the opaque insulating layer including a plurality of slots at predetermined locations; forming a photosensitive insulating layer on the substrate; illuminating the photosensitive insulating layer from light beams passing through the substrate and the first display electrodes in sequence with the opaque insulating layer as photo masks; removing the un-illuminated portion of the photosensitive insulating layer to form insulating ramparts; proceeding an anisotropic etching process to the opaque insulating layer for exposing the first display electrodes; forming an organic electroluminescent material on the exposed first display electrodes; and forming a plurality of second display electrodes on the organic electroluminescent material.
Additional advantages, objects and features of the present invention will become more apparent from the drawings and description which follows.